Process for reducing niobium oxides to metallic state



PROCESS FOR REDUCING NIOBIUM OXIDES TO METALLIC STATE Foord vonBichowsky, Wilmington, Del. 8 v

No Drawing. Application November 12, 1957 Serial No. 695,515

6 Claims. (Cl. 75-84) The present invention concerns an improved processfor the reduction of IllobllllIl oxygen compounds, that is thepentoxide, dioxide, oxide and/or sub-oxide to the metallic state by theemployment of hydrogen in conjunction with certain novel means.

It is known that niobium pentoxide in the presence of not less than byweight of pulverulent nickel when treated, in various kinds of furnacesand at above red heat, with pure hydrogen is reduced to the metallicstate. It also is known, in the absence of nickel, that the reactionapparently goes stepwise but at about 1100 C. 2

only to.a lower oxide of niobium with the formation of water vapor, asfollows:

I have now discovered, if the cited known methods and/ or others arecarried out in the presence of a catalytic agent or agents, that theabove proportions of added nickel may be diminished greatly and/or iteven may be present in such a form as to be readily separable from theresulting niobium powder by physical means, for example, by screeningand/or magnetically.

These surprising and commercially valuable results are obtained throughthe employment of a small amount of a compound or compounds of a metalof the alkali metal group, i. e. lithium, sodium, potassium, rubidiumand cesium. The last two members of that series, because of their cost,I use less frequently but they are not excluded in this process. Theabove alkali metal substances also may contain non-metallic elements,for example, oxygen, carbon and/or hydrogen and/ or a metallic element,e. g. niobium or calcium. When employing such compounds it often isdesirable to add or to have present a small amount of a substance whichby its removal during the heating and/or reduction of the niobium oxygencompound with'hydrogen will leave behind a permeable reducible mass.Such an aerating and/or spacing material may be, for example, carbon inone of its various forms or a non-agglutinative organic material, e. g.an organic acid say tartaric acid or the alkali and/or alkaline earthmetal salts thereof. Here the alkaline earth metal compound can be, forexample, calcium tartrate, acetate or carbonate which may serve as aspacer or an inhibitor of cohesion between the niobium produced and anyadded metal such as nickel. If desired the calcium carbonate may beemployed in company with sodium carbonate simply by saturating soda limewith carbon dioxide gas. The cited discoveries have their origin in thefollowing laboratory observations. I noted when an intimate mixture,containing approximately 96% of niobium pentoxide and 2% of sodiumcarbonate together with 2% of lampblack, all by weight, was placed in ametal boat of sheet nickel and heated in a stainless steel tube in thepresence of a current of purified hydrogen for 5 hours at 1050 C. andunder a positive pressure of about 25 mm. of Hg and thereafter wasallowed to cool quickly in the tube and in an inert atmosphere, that thecooled charge, where it was in contact with the bottom of the boat hadbeen reduced to silvery spots of metal but the boat itself wasunattacked.

In another experiment run under identical conditions but where theground mixture contained by weight of niobium pentoxide, 11% of nickelas the oxide (M 0 2% ofsodium carbonate and 2% lampblack the efliciencyof reduction was surprisingly high.

The extension of these laboratory observations to practical applicationmay be illustrated by the two following examples:

Example 1 There were ground together for 2 hours in a small ball mill,with enough mineral spirits to form a thin slurry,

10.0 g. pure niobium pentoxide 1.4 g. nickel oxide (Ni O 0.6 g. lithiumcarbonate 0.4 g. lampblack.

The resulting slurry was poured onto a suction filter and the filtercake placed in a large nickel combustion boat and dried. The boat wasinserted into a furnace made from a piece of stainless steel pipe or ofother material resistant to alkali fumes and heated, while displacingthe air with nitrogen, to about 500 C. whereupon the nitrogen wasreplaced by highly purified hydrogen and the temperature of the furnaceWas raised to about 1075 C. The flow of hydrogen was kept up until thegas leaving the furnace was free of water vapor. This usually requiredabout 24 hours. Then the tube furnace was cooled rapidly to roomtemperature, the hydrogen being displaced by pure argon during coolingto prevent the formation of any niobium hydride. The resulting niobiumpowder in the boat plus the metallic nickel then present could'becompacted into shapes by pressing or else the nickel could be removedfrom the powder by known means. The metal product after the removal ofany entrained catalyst was very pure and readily workable probably forthe reason that if any nitride nitrogen ever had been present in themetal it likely Was removed as a volatile cyanide through the combinedaction of the alkali metal carbonate and traces of residual carbon.

When the above experiment was carried out in accord with the procedureas given in Example 1 of my U. S. Patent No. 2,761,776 the run tooklonger, i. e. 30 hours and the end product was not as brilliant inappearance.

Example 2 10.0 g. pure niobium pentoxide 0.7 g. sodium carbonate 0.8 g.calcium carbonate were dry ground for an hour and the mixture thenmoistened and dried to a cake. This cake was broken up so that it passedthrough a 20 mesh screen. The granulated powder thereafter wastransferred to a vertical nickel tube with an internal diameter of about4 inch which tube contained, at the lower part of its heatable zone, 'aplug of line nickel screen. The air within that upright tube'wasdisplaced by nitrogen introduced below the porous plug of nickel screenand when the air was all driven out the nitrogen was replaced byhydrogen flowing upward at such a rate that the layer of niobium oxidemixture while undergoing heating was kept in gentle agitation orbubbling so that the charge came into very frequent and intimate contactwith the hot nickel tube and screen. The tube was heated to and kept atan operating temperature of about 1050 C, the rate of hydrogen ingressbeing adjusted to compensate for changes in its viscosity and density onheating and for any alterations 0 in the character of the bed.

At the end of about 30 hours the reduction was complete. The hydrogenthereupon was displaced by nitro- Patented Nov. 25, 1958 metal powderwas removed from the internally unaffected furnace tube and the calciumoxide extender and any residual sodium material were leached away,fonex'ample,

'by a diluted mineral-'01"weenie-aside. g. nitric or acetic acid andthen washed acid freeand dried.- d

Where a nickel or nickel linedtube isnotava'ilable for 1 the furnacesome nickel shot, eigl of'about l0 mesh'may be added to the charge andat the completion of the run these may be removed by screening. Theamount and/or 'size of shot added dep'ends'u'pon dimensional factors andis best determined by experiment but in anyevent the use of shot avoidsthe formation of such alloys as can form in the presence of compactedmixtures of excess, very finely divided nickel; In the placeof thecalcium carbonate or magnesium carbonate, carbonated soda lime may beemployed in equivalent amount.

In the preceding examples lithium carbonate and sodium carbonate havebeen'used as catalysts but similar potassium compounds may be employedespecially in the form of a comparable amount of the hexaniobate.

In this connection it should be noted that I have found 'a definite butwide limit as to the amount of alkali metal compound and/ or compoundsthat may be added. If too much be incorporated the reaction mass tendsto fuse and then is either no longer as permeable to the reducing actionof hydrogen or else the mass becomes so sticky when hot that a bubblingeffect is' nullified. For those reasons I prefer to add the alkalimaterial in an amount between 0.1% and 10% by weight of the niobiumoxide or oxides used. In some cases there is the possibility that thealkali metal or compound may be removed from the reaction zone byvolatilization but if this is suspected an ignition of the excitinghydrogen will show by the color of the flame whether the alkali isfuming off and if this fuming is excessive then the temperature can belowered slightly or the rate of hydrogen flow lowered or both. If therate of hydrogen flow be so high that the reduction efficiency is lowthen it can be advisable to recycle the exit gas after careful removalof the contained water vapor.

The examples specify the use .of pure niobium oxides but the commercialproducts, which may contain up to say 5% of associated tantalum oxideare not to be taken as excluded from the scope of the process.

Having now described my invention and some methods I for carrying itout, which methods are illustrative and are not to be considered asrestrictive, what I claim is:

1. Process for reducing niobium oxides to the metallic state whichcomprises the steps consisting in heating a niobium oxygen compound fromthe group consisting of the pentoxide, dioxide, oxide and sub-oxide,together with an alkali metal compound selected'from the groupconsisting of the carbonates, oxide, hydroxide, niobate and soda-lime'inan amount not exceeding 10% by weight of the niobium oxide together withan amount of a spacer material selected from the group consisting ofcarbon, calcium carbonate, magnesium carbonate, calcium tartrate andacetate, not exceeding 10% by weight of the niobium oxide, all theingredients being in contact with a nickelous material from the groupconsisting of nickel, nickel sesquioxide and nickelo-nickelic oxide andin permeable form while in a current of hydrogen at above red heat in areducing furnace with the exclusionof nitrogen and oxygen until thereduction is completed, then cooling the reduced product under inertconditions and separating the niobium metal containing product.

2. Process for reducing niobium oxidesto' the metallic state whichcomprises the steps consisting in heating a niobium oxygen compound fromthe group consisting of the pentoxide, dioxide, oxide, and sub-oxide,together with an alkali metal carbonate in an amount not exceeding 10%by weight of the niobium oxygen compound incorporated with an amount ofcarbon whose quantity does not exceed 10% by weight of the niobium oxideall the ingredients in permeable form being in contact with nickel whilein a current of hydrogen at about 1100 C. in a reducing furnace whileexcluding nitrogen and oxygen until the reduction is completed and thencooling the reduced metallized product under inert conditions andcomprising the final step of removing the residuum of undesiredingredients.

3. Process for reducing niobium oxides to the metallic state whichcomprises the steps consisting in heating a niobium oxygen compound fromthe group consisting of the pentoxide, dioxide, oxide, and sub-oxidetogether with lithium carbonate in amount not exceeding 10% by weight ofthe niobium oxide together with calcium carbonate in an amount notexceeding 10% by weight of the niobium oxide in'a currentof hydrogenwhilein contact with nickel'and in permeable form in a furnace to about1100 C. while excluding nitrogen and oxygen until the reduction iscompleted and then cooling the reduced product to room temperature underinert conditions-with the final step of extracting the finished product.

4. Process for reducing niobium oxides to the-metallic state whichcomprises the steps consisting in heating a niobium oxygen compound fromthe group consisting of the pentoxide, dioxide, oxide and sub-oxide,incorporated as permeable grains with sodium carbonate and calciumcarbonate in amounts each not exceeding l0% by weight of the pentoxidein a current of hydrogen while in intermittent contact with nickelwithin a furnace at about 1100 ,C. while excluding atmosphericcontaminants until reduction is completed and then cooling the reducedproduct under inert conditions to room temperature. and removing theresiduum of catalytic and spacer material by means of a weak acid leach.

5. Process for reducing niobium oxides to the metallic state whichcomprises the steps consisting inheating a niobium oxygen compound,specifically the pentoxide incorporated as permeable'grains with sodiumcarbonate and calcium carbonate in amounts each not exceeding 10% byweight of the pentoxide in a current of hydrogen while in intermittentcontact with coarser nickel particles and while within a furnace toabout 1050" C. while excluding oxygen and nitrogen until the reductionis completed and cooling the reduced mixture under inert conditions toroom temperature, then screening out the added coarse nickel particlesand eliminating the residiuum' of alkali and spacer material from theniobium powder by means of a weak acid leach.

6. Process for reducing niobium oxides to the metallic state whichcomprises the steps consisting in heating niobium pentoxide,incorporated as permeable grains with carbonated soda-lime whoseseparate content of sodium carbonate and calcium carbonate each do notexceed 10% by weight of the niobium oxide, in a current of hydrogenwhile in rapid intermittent contact with metallic I nickel, present as alining within a vertical reduction furtrace, to about 1050 C. whileexcluding oxygen and nitrogen until the reduction is complete andcooling the reduced product under inert conditions to room temperature,removing the residuum of alkali and spacer material from themetalliferous grains by-means of a weak acid leach and washing anddrying the .pure niobiumobtained.

References Cited in the file of this patent UNITED STATES PATENTS2,761,776 Bichowsky Sept. 4, 195 6

1. PROCESS FOR REDUCING NIOBIUM OXIDES TO THE METALLIC STATE WHICHCOMPRISES THE STEPS CONSISTING IN HEATING A NIOBIUM OXYGEN COMPOUND FROMTHE GROUP CONSISTING OF THE PENTOXIDE, DIOXIDE, OXIDE AND SUB-OXIDE,TOGETHER WITH AN ALKALI METAL COMPOUND SELECTED FROM THE GROUPCONSISTING OF THE CARBONATES, OXIDE, HYDROXIDE, NIOBATE AND SODA-LIME INAN AMOUNT NOT EXCEEDING 10% BY WEIGHT OF THE NIOBIUM OXIDE TOGETHER WITHAN AMOUNT OF A SPACER MATERIAL SELECTED FROM THE GROUP CONSISTING OFCARBON, CALCIUM CARBONATE, MAGNESIUM CARBONATE, CALCIUM TARTRATE ANDACETATE, NOT EXCEEDING 10% BY WEIGHT OF THE NIOBIUM OXIDE, ALL THEINGREDIENTS BEING IN CONTACT WITH A NICKELOUS MATERIAL FROM THE GROUPCONSISTING OF NICKEL, NICKEL SESQUIOXIDE AND NICKELO-NICKELIC OXIDE ANDIN PERMEABLE FORM WHILE IN A CURRENT OF HYDROGEN AT ABOVE RED HEAT IN AREDUCING FURNACE WITH THE EXCLUSION OF NITROGEN AND OXYGEN UNTIL THEREDUCTION IS COMPLETED, THEN COOLING THE REDUCED PRODUCT UNDER INERTCONDITIONS AND SEPARATING THE NIOBIUM METAL CONTAINING PRODUCT.